U.S. Pat. Nos. 5,201,186 and 5,222,368, which are assigned to the same assignee as the present application, disclose methods for detecting conditions which may cause shut down of a refrigeration unit, such as a transport refrigeration unit. When such a condition is detected, steps are taken to modify the operation of the refrigeration unit in an attempt to find an operating condition which will prevent, or at least delay, mandatory shut down. When mandatory shut down is still found to be required, an alarm code is stored which identifies the cause of shut down, and an alarm is generated which notifies a person in charge of the refrigeration unit, such as the driver of a truck or tractor-trailer unit which the refrigeration unit is associated with.
Certain types of refrigeration units, however, are required to reliably operate for relatively long periods of time without an attendant, such as transport refrigeration units which are associated with containers carried by rail. Application Ser. No. 245,266, filed May 18, 1994, which is assigned to the same assignee as the present application, is directed to improvements in such rail carried transport refrigeration units. The improvements include monitoring a predetermined parameter of the refrigeration unit. The refrigeration unit is shut down in the event the monitored parameter reaches a mandatory shut down condition, and a shut down count is incremented. The predetermined parameter is monitored during the forced shut down, and when the predetermined monitored parameter has a value which permits restarting of the refrigeration unit, the refrigeration unit is restarted when the value of the shut down count is less than a predetermined value. When restarted, the operation of the refrigeration unit is modified, with the modification being selected to reduce the probability of the monitored parameter reaching the predetermined shut down condition. In one embodiment, the high pressure side of the refrigeration unit is monitored. A shut down and subsequent re-start due to high pressure is accompanied by a modification in the operation of the refrigeration unit to reduce the load on the compressor. In another embodiment, the compressor is driven by an internal combustion engine monitored by a temperature sensor. In the event of a shut down and re-start due to an over-temperature condition of the engine, the operation of the refrigeration unit is modified to reduce the load on the engine.
U.S. Pat. No. 5,197,670, which is assigned to the same assignee as the present invention, teaches a transport refrigeration unit operable in a cycle mode. Prime mover re-start temperatures which define upper and lower limits of the off cycle or "null" band, are dynamically changed in response to a relationship between the temperature of a space being conditioned and ambient temperature.
An object of the present invention is to provide apparatus and methods which improve the reliability of transport refrigeration units having internal combustion engines as prime movers. Another object of the invention is to reduce the incidence of shut-downs of engine driven transport refrigeration units which operate unattended for long periods of time, such as the hereinbefore mentioned container units which are carried by rail, due to running out of engine fuel.